(1) Field of the Invention
This invention relates to an optical disc apparatus which records/reproduce information to/from a rotating circular-plate-shaped disc.
(2) Description of the Related Art
An optical disc apparatus refers to a data storage device which rotates a circular-plate-shaped disc which is a data recording medium, and then records data to the disc surface as well as reproduces data recorded on the disc surface.
An electronic component (optical head) includes a laser emitting unit, a laser receiving unit, an objective lens which focuses a laser beam onto a disc surface, and the like, to be used as a signal writing/reading unit for recording/reproducing data. The electronic component is called an optical pickup or simply a pickup. Examples of discs serving as a data recording medium include CD-ROM (Compact Disc Read Only Memory), CD-R (Compact Disc Recordable), CD-RW (Compact Disc Rewritable), DVD-ROM (Digital Versatile Disc Read Only Memory), DVD-R (Digital Versatile Disc Recordable), DVD-RW (Digital Versatile Disc Rewritable), DVD-RAM (Digital Versatile Disc Random Access Memory), DVD+R (Digital Versatile Disc Recordable), DVD+RW (Digital Versatile Disc Rewritable), BD-ROM (Blue-ray (trademark) Disc Read Only Memory), BD-R (Blue-ray (trademark) Disc Recordable), BD-RE (Blue-ray (trademark) Disc Rewritable) and the like. In general, the optical disc apparatus is installed in electronic equipment including a CPU (Central Processing Unit) which performs access control to the optical disc apparatus, operation processing and the like, such as, for example, a PC (Personal Computer).
When the electronic equipment is a desktop PC, the optical disc apparatus used is of the generally so-called half-height type. When the electronic equipment is a notebook PC, the optical disc apparatus used is of the generally so-called slim type.
In the optical disc apparatus, in particular, a larger data storage capacity has been recently required. To achieve the increase in storage capacity, it is necessary to use a large capacity disc such as BD and also to increase the number of disc recording layers such as double layer structure.
That is, for supporting all types of data recording media such as CD/DVD and BD, an optical disc apparatus needs to include a BD-dedicated lens in addition to a CD/DVD-dedicated lens, as an objective lens which is mounted on a position of an optical pickup close to and opposite to the disc recording surface, in order to focus both the CD/DVD red laser light and the BD blue laser light onto the disc recording surface.
In this connection, the objective lens is controlled in its position and its angle relative to the disk recording surface while the disc is rotated. For this purpose, in general, the object lens is secured to a supporting member which is held in the air by a flexible material such as a metal wire. A copper wire is wound around the supporting member so as to form a coil, and also two pairs of permanent magnets are placed on opposite sides of the supporting member. As a result, the supporting member is located in a magnetic field, so that an electromagnetic force is produced by the passage of electric current through the copper wire wound in a coil form in order to control the position and the angle of the supporting member. A mechanism for controlling a position and an angle of an objective lens is herein referred to as an “objective-lens drive mechanism”.
As described above, an increase in storage capacity involves the necessity for providing two objective lenses for CD/DVD and BD. This increases the own weight of the supporting member, causing an increase in the amount of current passing through the coil for driving the supporting member increased in own weight, which in turn increase the amount of heat dissipated from the coil. Thus, a temperature rise occurs in the objective lens fitted in the supporting member, and the thermal deformation of the lens causes the deviation of the optical axis of the laser light, resulting in a significant reduction in recording quality.
In terms of cost reduction, plastic is more preferable to glass for a material for the objective lens. In this case, the thermal deformation of the lens is more noticeable, leading to a further apparent reduction in recording quality caused by the deviation of the optical axis of the laser light. In particular, the slim-type optical disc apparatus has a smaller-volume, higher-dense apparatus housing than that of the half-height-type optical disc apparatus. For this reason, the objective-lens drive mechanism equipped with an objective lens is exposed to a higher-temperature atmosphere as compared with that of the half-height-type optical disc apparatus.